Thyroid cancer incidence rates have been increasing for the last 3 decades in the US and the reasons for this are largely unknown. We have been studying potential risk factors for the disease in a pooled analysis of 5 NCI prospective studies. This pooling project provided some of the strongest evidence to date that obesity may be a risk factor for thyroid cancer and the rising obesity rates could therefore be part of the explanation for the rise in thyroid cancer incidence rates. We are now expanding this pooling project to include data from 15 European and US cohorts to examine the relationship in more detail including the risk associated with central adiposity and the relationship between obesity and rarer thyroid cancer subtypes. NCI Cohort Consortium BMI Pooling Project - We built a rich dataset of lifestyle risk factor and mortality data from 20 prospective studies and over 1.5 million people to study the relationship between BMI and all cause mortality. The results from this detailed analysis published in 2010 suggested that optimal BMI was in the range 20-25. We are currently exploring the association between waist circumference and all cause mortality, and expanding the pooling project to look at cancer incidence for rare cancers including thyroid and gallbladder. These cancers are typically difficult to study in individual cohorts because the numbers of cases is limited. Childhood Cancer In Chinese Children and Family Cohorts -We are conducting two pilot studies to test the feasibility of (1) follow and participation in interviews of a sample of 500 families from two county sites where the Community Intervention Program (CIP) was carried out in the mid-1990s and (2) identification of incident pediatric cancers arising among thoseborn during 1994-96 in hospitals serving the CIP population and ability to link these pediatric cancer patients back to the CIP population. The CIP community intervention program trial, which was carried out during 1994-96 in three large counties northeast and south of Beijing, evaluated the effectiveness of periconceptional folic acid supplements in reducing neural tube defects. There were dramatic reductions in neural tube defects among offspring of mothers who took folic acid supplements during the periconceptional period. Publications from case-control epidemiologic studies in the past 10 years from Western countries have shown that periconceptional folic acid supplements may reduce risks of pediatric leukemia and potentially other pediatric cancers in offspring of mothers who take these supplements. Other studies have shown statistical associations with periconception folic acid and other serious chronic diseases of offspring including asthma. The pilot studies will attempt to trace, enroll, and interview 500 families from Taicang, Jiangsu Province and Laoting, Hebei Province and will seek to identify all pediatric cancers diagnosed during 1994 to the present among children born during 1994-96 and link these children back to the CIP cohort.